ESA finds O2 for the first time on a comet

The European Space Agency (ESA) announced that the Rosetta Mission, orbiting since August 2014, found oxygen in the atmosphere of the comet 67P (Churyumov-Gerasimenko).

The spacecraft, using the ROSINA mass spectrometer, found a molecule of oxygen (O2), as well as a series of different gases pouring from the comet’s nucleus, such as water vapour, carbon monoxide and carbon dioxide. Other components like nitrogen, sulphur and noble gases were also registered by the spectrometer.

The results shown in the graphic are based on data collected by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis Double-Focusing Mass Spectrometer (ROSINA-DFMS) between September 2014 and March 2015 when Rosetta was still on the approach to the Sun along its orbit. Credit: ESA

“It’s unanticipated because there aren’t very many examples of the detection of interstellar O2. And thus, even though it must have been incorporated into the comet during its formation, this is not so easily explained by current Solar System formation models,” said Kathrin Altwegg, principal investigator of ROSINA, in the press release.

Although oxygen is the third most common element found in the Universe, the oxygen molecule is hard to find, due to its reactive behavior that makes it break apart to form other molecules. Although it has been found in places such as the icy moons of Saturn and Jupiter, O2 wasn’t detected on comets until now.

Analyzing nearly 3,000 samples taken from the comet between September 2014 and March 2015, scientists found the oxygen particle in a higher magnitude than the measure predicted by previous models and simulations.

The results, published in the Journal Nature, show a relationship with the amount of water measured by researchers, suggesting that the cause of the origin of the molecule on the nucleus, and the release mechanism of release are related.

Scientists tried to explain that O2 is the final product of the process of photolysis and radiolysis that takes place on the icy water surfaces in the comet, a consequence of the daily sublimation-condensation process of the comet —what is called its “water cycle”.

“We found a mechanism that replenishes the surface of the comet with fresh ice at every rotation: this keeps the comet ‘alive’. When the Sun was shining on these regions, the ice was gone. This indicates a cyclical behaviour of water ice during each comet rotation,” explained De Sanctis, a scientist from the ESA, last September.

How can photolysis and radiolysis explain the formation and liberation of O2? By photolysis, the bonds between molecules are broken, as radiolysis gets photons, electrons and ions to apply energy into the icy surface, leading to its release. These are processes previously observed on moons and Saturn’s rings.

Nevertheless, the researchers discarded radiolysis as an explanation, because the products of the process should have been released a long time ago —when the comet engaged its orbit. So, these both processes explain the first appearances of O2 but fail to answer why they are still being released from the comet.

However, Andre Bieler, from the University of Michigan and lead author of the paper, explains that it is possible that the O2 forming the ice millions of years ago can be released today in the form of water vapour, as the comet gets through different light conditions.

Scientists believe that, regardless of how the process works today, the O2 was “protected” from being “destroyed” by future chemical reactions. Moreover, they affirm that these findings can have multiple implications on the conception of how the Solar System was created and its evolution.